One of the most important requirements of a next generation wireless communication system is to support a required high data rate. For this, various techniques such as multiple input multiple output (MIMO), cooperative multiple point transmission (CoMP), relay, etc., have been under research, but the most fundamental and reliable solution is to increase a bandwidth.
However, a frequency resource is in a saturation state at present, and various schemes are partially used in a wide frequency band. For this reason, in order to ensure a wideband bandwidth in order to satisfy a required higher data rate, a system is designed to satisfy a basic requirement which requires separate bands capable of operating respective independent systems, and a carrier aggregation (CA) is introduced. In concept, the CA aggregates a plurality of bands into one system. In this case, a band that can be independently managed is defined as a component carrier (CC).
To support growing transmission capacity, the 3GPP LTE or the 802.16m has recently expanded its bandwidth to 20 MHz or higher. In this case, a wideband is supported by aggregating one or more CCs. For example, if one CC corresponds to a bandwidth of 5 MHz, four carriers are aggregated to support a bandwidth of up to 20 MHz.
As such, a plurality of CCs are used in the carrier aggregation system. A method of receiving control information of a user equipment (UE) may be problematic in the carrier aggregation system. In the conventional system using a single carrier, for example, in an LTE system, the UE first receives a system band of the carrier, the number of antenna ports, a transmission mode, etc., from a base station (BS) as system information, and then performs blind decoding on control information. That is, the UE performs decoding in accordance with the number of various cases and receives/confirms control information of the UE by using cyclic redundancy check (CRC) or the like in a state where the UE does not know an exact control information format transmitted in a control region of a subframe and does not know a specific station from which control information is transmitted. When the conventional method of receiving control information is equally applied to the carrier aggregation system, the number of blind decoding attempts of the UE may increase, which may result in a problem such as power consumption of the UE, decrease in a decoding rate, etc.
Accordingly, there is a need for a method for transmitting control information of a BS in a carrier aggregation system, a method for receiving control information of a UE, and the UE using the methods.